1 files changed, 25 insertions, 11 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 830893b2b3c7..0713bfbf0954 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -201,6 +201,18 @@ static unsigned long highmem_dirtyable_memory(unsigned long total)
                      zone_reclaimable_pages(z) - z->dirty_balance_reserve;
         }
         /*
+         * Unreclaimable memory (kernel memory or anonymous memory
+         * without swap) can bring down the dirtyable pages below
+         * the zone's dirty balance reserve and the above calculation
+         * will underflow.  However we still want to add in nodes
+         * which are below threshold (negative values) to get a more
+         * accurate calculation but make sure that the total never
+         * underflows.
+         */
+        if ((long)x < 0)
+                x = 0;
+
+        /*
          * Make sure that the number of highmem pages is never larger
          * than the number of the total dirtyable memory. This can only
          * occur in very strange VM situations but we want to make sure
@@ -222,8 +234,8 @@ static unsigned long global_dirtyable_memory(void)
 {
         unsigned long x;
 
-        x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() -
-            dirty_balance_reserve;
+        x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages();
+        x -= min(x, dirty_balance_reserve);
 
         if (!vm_highmem_is_dirtyable)
                 x -= highmem_dirtyable_memory(x);
@@ -290,9 +302,12 @@ static unsigned long zone_dirtyable_memory(struct zone *zone)
          * highmem zone can hold its share of dirty pages, so we don't
          * care about vm_highmem_is_dirtyable here.
          */
-        return zone_page_state(zone, NR_FREE_PAGES) +
-               zone_reclaimable_pages(zone) -
-               zone->dirty_balance_reserve;
+        unsigned long nr_pages = zone_page_state(zone, NR_FREE_PAGES) +
+                zone_reclaimable_pages(zone);
+
+        /* don't allow this to underflow */
+        nr_pages -= min(nr_pages, zone->dirty_balance_reserve);
+        return nr_pages;
 }
 
 /**
@@ -1069,7 +1084,7 @@ static void bdi_update_bandwidth(struct backing_dev_info *bdi,
 }
 
 /*
- * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
+ * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
  * will look to see if it needs to start dirty throttling.
  *
  * If dirty_poll_interval is too low, big NUMA machines will call the expensive
@@ -1436,9 +1451,8 @@ static DEFINE_PER_CPU(int, bdp_ratelimits);
 DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
 
 /**
- * balance_dirty_pages_ratelimited_nr - balance dirty memory state
+ * balance_dirty_pages_ratelimited - balance dirty memory state
  * @mapping: address_space which was dirtied
- * @nr_pages_dirtied: number of pages which the caller has just dirtied
  *
  * Processes which are dirtying memory should call in here once for each page
  * which was newly dirtied.  The function will periodically check the system's
@@ -1449,8 +1463,7 @@ DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
  * limit we decrease the ratelimiting by a lot, to prevent individual processes
  * from overshooting the limit by (ratelimit_pages) each.
  */
-void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
-                                        unsigned long nr_pages_dirtied)
+void balance_dirty_pages_ratelimited(struct address_space *mapping)
 {
         struct backing_dev_info *bdi = mapping->backing_dev_info;
         int ratelimit;
@@ -1484,6 +1497,7 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
          */
         p = &__get_cpu_var(dirty_throttle_leaks);
         if (*p > 0 && current->nr_dirtied < ratelimit) {
+                unsigned long nr_pages_dirtied;
                 nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
                 *p -= nr_pages_dirtied;
                 current->nr_dirtied += nr_pages_dirtied;
@@ -1493,7 +1507,7 @@ void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
         if (unlikely(current->nr_dirtied >= ratelimit))
                 balance_dirty_pages(mapping, current->nr_dirtied);
 }
-EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
+EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
 
 void throttle_vm_writeout(gfp_t gfp_mask)
 {